Hardtops: Extra Weight or Aerodynamic Advantage?
Slideshow: We look at an aerodynamic study to determine the difference between top-down cruising and track day blasting.
Hardtop Droptop
Mustangs are often modified in convertible and coupe form alike. Some people prefer the feel of the open road while others prefer to be cocooned underneath a roof that provides aerodynamics advantages as well as shielding from the elements. Both have their perks, but we’ll look at things through data backed studies to confirm just how much potential advantage a hard top has.
image courtesy of squir.com
More Than You Think
According to data obtained by Aniket A. Kulkarni, S.V. Satish and V. Saravanan at the PES Institute of Technology the coefficient of drag on a CFD modeled car increased from 0.75 to 0.97 after the convertible top was lowered. While this is nowhere near a modern Mustang’s coefficient of drag—they’re much more slippery—it does give a decent understanding of what happens when the top goes down.
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Hardtop Advantages?
As air passes over the windshield of your car it increases in pressure and speed. This fast-moving air then travels over the roof of the car which causes lift. Lift is bad. Manufacturers work hard to minimize this and when you drop the top on a car you essentially disrupt the flow they have worked on sculpting. Turbulent air doesn’t flow as smoothly causing drag and sucking up previous horsepower.
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Other Gains
From a structural standpoint, hardtops tend to have more rigidity than a soft top which helps keep tires and suspension components operating as they were intended to. Any time you have excessive chassis flex the tires will fight to maintain their contact patch. Furthermore, the moment you introduce a rear wing or time attack style aerodynamics it becomes very important to give the air something to hold onto. When it comes to performance you want a sealed roof.
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Wing Control
Rear wing efficiency has a lot to do with how air is flowing before it gets to the wing itself. Trying to make downforce by using turbulent air isn’t the best way to go about things so a hard top that smooths outflow will help in creating meaningful use of any well-designed aftermarket parts you choose to slap onto you track weapon. Although, this doesn’t stop some enthusiasts from throwing a pep boys wing on the back and claiming they make real downforce.
image courtesy of flickr.com
Summary
If you were going to buy any Mustang for the track then a hard top is really the only way to go. Small things like removing side mirrors or shaving door handles can also have an effect on airflow, but it’s going to be hard to beat smooth flow over a solid roof. The moment you introduce a rear wing / front splitter combination this becomes even truer. Hope you enjoyed.
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